Electronic airflow control systems, such as variable cam timing, systems and electronic throttle control systems, replace traditional mechanical throttle cable systems with an "electronic linkage" provided by sensors and actuators in communication with an electronic controller. This increases the control authority of the electronic controller and allows the airflow and/or fuel flow to be controlled independently of the accelerator pedal position.
To control the actual output engine brake torque to achieve the driver demanded engine brake torque, it is desirable to calculate a corresponding desired airflow and fuel flow. Preferably, this computation accounts for variations in engine operating parameters, such as engine operating temperature and accessory losses.
Prior art approaches convert the desired engine torque to a desired airflow using a two-dimensional lookup table with inputs for desired torque and engine speed. However, such lookup tables are typically calibrated for stoichiometric operation and for maximum brake torque (MBT). The resulting desired airflow is then modified by a function which relates engine operating temperature and air/fuel ratio to engine torque to generate a modified or corrected airflow. The corrected desired airflow is then achieved via an appropriate airflow rate controller. This approach may be seen by reference to U.S. Pat. Nos. 5,351,776 and 5,383,432, for example.
While the prior art approaches may be acceptable for many applications and operating conditions, it is desirable to provide a more robust engine torque controller which improves powertrain is performance for current applications and is more amenable to new engine technologies and control strategies such as direct injection, lean burn, variable cam timing, and variable displacement applications.